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Active Directory / Office 365

5 Key Office 365 Migration Reminders

5 Key Office 365 Migration Reminders
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Microsoft wants your migration to Office 365 to go as smoothly as possible.  They’ve spent a great deal of time working on making it a streamlined process with fewer errors to worry about.  Recently Microsoft released a new Hybrid Agent public preview that is part of the Office 365 Hybrid Configuration Wizard and allows you to choose between an Exchange Classic Hybrid Topology and an Exchange Modern Hybrid Topology.  Learn more about this new Hybrid agent here.

Prior to making the move to Office 365, I like to give a few recommendations depending on the size of your organization and the current configuration with your on-premises Exchange environment.  Here are 5 reminders:

  1. Revise Legacy Domains:  Many organizations are still working off legacy domain design that goes back nearly a score (20 years) to when Windows 2000 Active Directory was first released.  Every location has a domain.  Every department has a domain.  Every person has a domain (kidding… let’s hope that’s not accurate).  With a move to Office 365, you’re going to be connecting your on-prem AD and Exchange up to Azure AD and Exchange Online.  If you were ever going to look at restructuring now is the time.  There are a variety of different tools to help you accomplish this and a free one is the Active Directory Migration Tool.  It has its issues but hey… it’s free… and I’ve personally used it to get the job done (65 domains down into 1!)
  2. Use the Deployment Assistant:  This is yet another free tool that I’ve been promoting for many years.  Many IT admins have NEVER heard of it.  And you wouldn’t if you aren’t migrating often.  But if you’re ready to make the move this tool is a life saver.  You answer a few basic questions about what you have and what you’re going to and you are given back a checklist of things to remember connected to articles that tell you how to perform each task.  This will ensure you don’t forget an essential step in the process.
  3. Move Services First:  With on-premises Exchange we surrounded our server(s) with an ecosystem set of solutions from a variety of third-party providers.  Moving the cloud gives Microsoft a chance to fill in some of those gaps for you.  But it may be that you still seek third-party bridges for those gaps in areas like security, archive, backup/recovery, monitoring and so on.  It’s not a good idea to daisy chain multiple points on to the front of Office 365 (latency and points of failure woes can result) so choose your all-in-one bolt-on solution wisely.  And before you move a single mailbox make sure your services are in place.  Think of it like this… if you were moving houses and your current house is very well protected.  Would you move your boxes into the new house before the electricity, security system, Internet, cameras, etc. were set up and working?  Probably not.  So before you move mailboxes to the cloud, make sure you have a 1 to 1 set of expectations from on-prem to cloud with regard to your necessary services.
  4. Mail Flow Tipping Points:  Initially you might configure your environment to continue to receive email on-prem and send up to the mailboxes in Office 365.  At some point, you’ll want to switch that and have that mail go through Office 365 and down.   Keep track of your migration to ensure you know when that point is.  Also, it’s good to know that if you are using an Edge Transport Server for address rewrite scenarios you’ll need to either a) stop doing address rewrite b) keep mail flow going out through the Edge server (because O365 doesn’t do address rewrite) or c) get a third party solution that can handle this for you.
  5. Thoroughly test that your hybrid works.   Confirm mailbox creation, verify mail flow and so on.  Don’t forget to migrate a mailbox from on-prem to the cloud to ensure every piece is solid.  Fellow MVP Paul Cunningham has a script that tests federated domain proof TXT records quite easily and you might want to try it out.

Obviously, 5 reminders isn’t an exhaustive list.  But it might just get you pointed in the right direction on a few things that you hadn’t considered before.  Hopefully, that is the case.

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Co-founder of and Microsoft Office 365 MVP, InfoWorld columnist (Enterprise Windows), and Mimecast consultant.

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